Inhibitory effects of synthetic and natural colorants on carcinogenesis VI

ABSTRACT

A method of reducing the percentage of Epstein-Barr virus genome-carrying cells which exhibit Epstein-Barr virus early antigen induction, wherein the Epstein-Barr virus genome-carrying cells have been cultivated in the presence of a tumor-promoting chemical and/or a tumor-inducing chemical. The method is performed by: 
     a) cultivating Epstein-Barr virus genome-carrying cells in the presence of a tumor-promoting chemical and/or a tumor-inducing chemical; and 
     b) treating the Epstein-Barr virus genome-carrying cells with a synthetic anthraquinone colorant containing a sulfonated phenylamino group. The colorant is effective to reduce the incidence of Epstein-Barr virus early antigen induction in the cultivated Epstein-Barr virus genome-carrying cells.

This application is a divisional application of U.S. application Ser. No. 08/845,166, filed Apr. 21, 1997, which in turn claims the benefit of U.S. Provisional Application No. 60/022,638, filed Jul. 24, 1996.

FIELD OF THE INVENTION

The field of the invention relates to use of food colorants in the treatment or prevention of cancer. More particularly, the invention relates to use of safe, nontoxic food colorants to inhibit carcinogenesis. The food colorants may be natural pigments extracted from a plant or plants, or they may be synthetic compounds approved by the FDA for use as food colorants or food dyes.

BACKGROUND OF THE INVENTION

A wide variety of colorants have been approved by the FDA for use in foods, pharmaceuticals, and cosmetic preparations. Extensive toxicity studies have been performed on each of these compounds, and they have been found to be nontoxic. However, relatively little research has been performed to determine whether use of these food colorants in foods, drugs, and cosmetics is actually beneficial, rather than simply not harmful.

We have been conducting studies designed to help fill this gap. Our research is directed towards use of natural and synthetic food colorants in the inhibition of carcinogenesis. In past work, we have described inhibition of tumor formation by natural colorants and extracts of fruits, vegetables, and other plant parts (Kapadia et al., Proc. Int Congress on Nat. Prod. Research, Abstract No. 225; Halifax, Canada; 1994). Extracts of turmeric, paprika, and annatto seeds have been found to be of great interest, particularly in the prevention of cancer. Paprika extracts, obtained from Capsicum anrum L. (Fam: Solanacaea), are among the oldest and most important carotenoid extracts. The main carotenoids present in paprika are capsanthin (I) and capsorubin (II), largely as their acyl esters. Other minor components are present.

Annatto seeds are the seeds of the tropical bush Bixa orellana L. (Family: Bixacaea). The major pigment in the carotenoid cis-bixin (III), the monomethyl ester of diapocarotenoic acid (IV; also known as cis-norbixin). Trans-bixin and cis-norbixin are also present as minor constituents. Trans-bixin and cis-bixin are both sparingly water-soluble, and may be converted to a water-soluble salt of the corresponding norbixin upon alkali hydrolysis.

(III; R═CH₃)

(IV; R═H)

Turmeric, also called curcuma, is a fluorescent yellow-colored extract from the rhizomes of several species of the curcuma plant. Curcuma longa is the usual commercial source. The pigments curcumin (V), demethoxycurcumin (VI), and bisdemethoxycurcumin (VII) occur in every species, together with minor ingredients that contribute to the flavor.

(V;R′═R″═OCH₃)

(VI;R′═H,R″═OCH₃)

(VII;R′═R″═H)

Other natural colorants that have been found to be of interest include the betanins and the anthocyanins. Betanins may be readily extracted from beet roots, and anthocyanins may be extracted from grapes, red onion skin, cranberries, and other plant-derived materials.

The studies reported herein include in vitro studies of inhibition of Epstein-Barr virus early antigen (EBV-EA) induction studies by synthetic colorants and by natural plant extracts and colorants. The Epstrin-Barr virus (EBV)is a member of the herpes virus family, and has been implicated in the pathogenesis of Burkitt's lymphoma, nasopharyngeal carcinoma, and B lymphocyte neoplasms. Infection of a human by EBV is commonly followed by a latency period, when the virus is present intracellularly in an unexpressed state. T cell suppressor mechanisms of the immune response to the EBV are effective in the inhibition of acute EBV infection. If these mechanisms fail, Burkitt's lymphoma, nasopharyngeal carcinoma, and B cell lymphomas may emerge. This is a serious problem during the postoperative recuperation period following organ transplants, as immunosuppresive therapy is often used to prevent rejection. It is therefore important to find new cancer chemopreventive agents which prevent formation of tumors linked to the Epstein-Barr virus. In vitro inhibition of EBV-EA induction in Epstein-Barr virus genome-carrying cells by a potential cancer chemopreventive compound serves as an excellent sign that the compound may inhibit tumor formation in a living organism. In fact, inhibitory activity toward EBV-EA induction is often taken as a measure of anti-tumor promoting activity.

In vivo studies of inhibition of skin tumor formation by synthetic and natural colorants were also performed, using a two-stage mouse skin carcinogenesis test. A diagram illustrating such a test is provided in FIG. 1. Studies on rats and mice provide insight into the cancer induction process in humans and animals. Two mice (or groups of mice) are each treated with a compound known to initiate tumor formation (stage 1). In FIG. 1, 7,12-dimethylbenz[α]anthracene (DMBA) is used as the tumor initiator; other compounds may be used. The mice are then subjected to a condition or compound on a continued basis that promotes tumor formation (stage 2). Ultraviolet B radiation serves as an effective tumor promoter, as shown in FIG. 1. Topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) also serves as a promoter of skin tumors. One animal, the test animal, is provided an inhibitor of tumor promotion. The inhibitor may be provided in drinking water or topically applied to the skin. The other animal, the control animal, is provided with no inhibitor. At the end of a defined period, the number of tumors on the test animal is compared to the number of tumors on the control animal. Similar tests were performed for inhibition of pulmonary tumor formation, using injected 4-nitroquinoline 1-oxide as a tumor initiator and glycerol, provided in drinking water as a tumor promoter.

In EMF Health Report, vol. 1, No. 2 (1993), cancer initiators are defined as compounds that cause genetic damage. Only a single exposure is required to start the cancer-forming process. Compounds which initiate tumor formation include nitrosamines, alkylating agents, aromatic amines, polycyclic aromatic hydrocarbons, dimethylbenz[α]anthracene, vinyl chloride, asbestos, N-methyl-N-nitrosourea, and azaserine, as disclosed in Advances in Cancer Research, vol. 50, pp. 26-30.

In EMF Health Report, vol. 1, No. 2 (1993), cancer promoters are defined as compounds that cause irritation, inflammation, and cell growth when applied to an animal alone, and which increase the rate of tumor growth when applied after exposure to an initiator. Compounds which initiate tumor formation include active phorbol esters, such as tetradecanoylphorbol acetate and phorbol dibenzoate; teleocidin and related compounds; aplysiatoxin and related compounds; mezerein; tetradecanoyl ingenol; iodoacetic acid; benzoyl peroxide; palytoxin; and anthralin. These promoters are disclosed in Biomedicine & Pharmacotherapy, vol. 42, pp. 447-450, and in Advances in Cancer Research, vol. 50, pp. 26-30 (1987).

The phrases “chemical substance selected from the group consisting of tumor promoters and tumor initiators” is intended to encompass those compounds specifically named in Exhibits B-D. Those compounds which fall under the definitions provided in EMF Health Report, vol. 1, No. 2 (1993), and which a worker of ordinary skill in the art would have known to be a functional equivalent of a phorbol ester tumor promoter or a dimethylbenz[α]anthracene tumor promoter, are also included.

SUMMARY OF THE INVENTION

A first object of this invention is to evaluate a series of FDA-approved synthetic food colorants for inhibitory effects on carcinogenesis. The colorants were tested using in vitro assays for inhibition of Epstein-Barr virus early antigen (EBV-EA) induction in cells exposed to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). High inhibitory activity toward EBV-EA induction is known to be indicative that a composition has potential utility as an anti-tumor promoting or cancer chemopreventive agent. Epstein-Barr virus genome-carrying lymphoblastoid cells (Raji cells) were used in the in vitro studies.

Synthetic food colorants which were found to be particularly effective as inhibitors of EBV-EA induction include:

a) sulfonated azo compounds having formula VIII:

and wherein R₁ is —H, lower alkyl, lower alkoxy, —CO₂H, or —SO₃M; R₂ is —H, lower alkyl, or —SO₃M; R₃ is —H, lower alkyl, or —SO₃M; R₄ is —H, —CO₂M; or —SO₃M; R₅ and R₆, which may be the same or different, are independently selected from the group consisting of —H, —OH, —NL₂, —CO₂M, or —SO₃M; L is —H, lower alkyl, or lower hydroxyalkyl, and M is —H, an alkali metal cation, or an alkaline earth metal cation;

b) colorants of formula IX and alum lake colorants derived from colorants of formula IX:

wherein X is —NH— or —S—, R₇ is —H or lower alkyl; R₈ is —H or —SO₃M; R₉ is —H or —Cl; and M is —H or an alkali metal cation;

c) colorants of formula X:

wherein R₁₀ is —H or —OH and each R₁₁ is a lower alkyl group;

d) fluorescein derivatives of formula XI:

wherein Y is —H or —Br, and

fluorescein derivatives of formula XII:

wherein Z is —H, —Br, or —I;

e) anthroquinone derivitives including dyes of formula XIII:

wherein R₁₂ is —H or lower alkyl and L is —OH or

and

f) a pyrene derivative of formula XVI:

Although other synthetic colorants were effective as well, aromatic azo compounds, or azo dyes, which contain acidic or anionic groups appear to be of particular utility in inhibition of carcinogenesis. Some of the synthetic colorants which exhibited measurable inhibition of EBV-EA induction were then bioassayed to determine whether they inhibited TPA-promoted carcinogenesis in epidermal tissue. It was found that colorants which were tested in the bioassay appear measurably inhibit formation of chemically-promoted skin tumors.

A second object of the invention is to evaluate a series of plant extracts for inhibitory effects on carcinogenesis. The in vitro inhibitory effects of the beet root extract and of grape extract on Epstein-Barr virus early antigen induction in Raji cells exposed to the tumor promoter TPA were assayed, and found to show significant anti-tumor promoting activity. In fact, the inhibitory activity of beet root extract was found to be greater than that shown by extracts of red bell peppers, red onion skin, paprika, and cranberries. In vivo studies of carcinogenesis inhibition by beet root extract were then performed. When beet root extract was given orally to mice, formation of skin tumors promoted by topical application of TPA or by exposure to UV radiation was significantly reduced. Also, beet root extract given orally reduced the incidence of glycerol-promoted pulmonary tumor formation.

Research was also done on natural food colorants extracted from turmeric, annatto seeds, and paprika. These colorants are commercially available in a variety of formulations in aqueous, vegetable oil, or propylene glycol vehicles. These vehicles may also contain emulsifiers and/or dispersants such as polysorbate 80 and lecithin. Recent studies have reported that colorants derived from turmeric, annatto, and paprika inhibit carcinogenesis. In the work described herein, the anti-tumor promoting activity of over thirty natural colorant formulation was investigated. Many of these formulations were found to exhibit significant in vitro inhibition of EBV-EA activation in Raji cells. However, many of these formulations exhibited cytotoxicity, suggesting that use of these compositions to inhibit tumor formation may pose hazards to human health. Fortunately, some compositions which inhibited EBV-EA activation without exhibiting cytotoxicity were identified. The most effective of these compositions were;

a) a mixture of natural extractives of annatto seeds and turmeric with polysorbate 80, potassium hydroxide, and propylene glycol; and

b) a natural extractive of paprika in vegetable oil.

In vivo studies indicate that oral feeding of paprika and annatto extracts acts to inhibit TPA-induced skin tumor formation. They were also found to be effective anti-inflammatory agents.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the method used to perform a bioassay for anti-tumor promoting activity using a two-stage mouse skin carcinogenesis test.

FIG. 2 shows the inhibitory effect of the synthetic colorants tartrazine and erythrosine B on TPA-promoted mouse skin tumor promotion.

FIG. 3 shows the inhibitory effect of beetroot extract (betanin) on TPA-promoted mouse skin tumor promotion.

FIG. 4 shows the inhibitory effect of beetroot extract (betanin) on ultraviolet B radiation-promoted mouse skin tumor promotion.

FIG. 5 shows the spleens of mice subjected to UV radiation treatment for twenty weeks. Those from mice maintained on water alone show pronounced enlargement (splenomegalia); those from mice maintained on water containing 0.0025% betanin do not.

FIG. 6 shows the inhibitory effect of natural extracts of annatto seeds and paprika on TPA-promoted mouse skin tumor promotion.

DETAILED DESCRIPTION OF THE INVENTION 2. In Vitro Studies on Inhibition of Carcinogen's in Mice

1.1 Materials and Methods

In vitro studies were carried out using an Epstein-Barr virus (EBV) early antigen induction assay performed in the following manner. EBV genome-carrying lymphoblastoid cells (Raji cells) were cultivated in an RMPI 1640 medium. The indicator cells were incubated at 37° C. for 48 hours in 1 ml of the medium. The medium also contained the tumor promoter TPA (20 ng/ml, or 32 pM), the tumor co-inducer butyric acid (4 mM), and a known amount of test dye in dimethylsulfoxide (DMSO). Smears were then made from the cultured cell suspension. The cells exhibiting EBV activation in each smear were stained by high titer EBV-positive sera from nasopharyngeal carcinoma patients and detected using conventional indirect immunofluorescence techniques. In each assay, at least 500 cells were counted and the experiments were repeated at least twice. The average EA induction of each assay was compared to that of a positive control experiment. In the control experiment, Raji cells were incubated at 37° C. for 48 hours in 1 ml of the medium. The medium also contained the tumor promoter TPA (20 ng/ml, or 32 pM) and the tumor co-inducer butyric acid (4 mM). In the control experiments, EA induction was normally around 30%.

In order to determine whether or not the synthetic colorants tested in the EBV-EA activation tests exhibited unacceptable cytotoxicity, cell viability tests were performed using the trypan-blue staining method. After the EBV-EA activation test, 0.1 ml of a suspension of treated cells from the EA induction test in phosphate buffer solution was stained with 0.1 ml of a 0.25% trypan-blue solution. Dying cells were dyed blue. Non-dyed cells were counted. If more than 40% of cells were dyed blue (that is, fewer than 60% of the cells were living, viable cells), the cytotoxicity of the test compound used in the EA induction test was judged to be unacceptably high.

The synthetic colorants which were tested for inhibition of EBV-EA induction using the assay techniques described above were obtained as gifts from the following sources:

a) Dr. A. Weiss Food and Drug Administration Center for Food Safety and Applied Nutrition Office of Cosmetics and Colors Washington, D.C.

b) Crompton and Knowles Corp. Mahwah, N.J.

c) Hilton Davis Co. Cincinnati, Ohio

d) Pylam Products Co., Inc. Garden City, N.Y.

The plant-derived colorant formulations which were tested for inhibition of EBV-EA activation by the described techniques are listed in Tables 1 and 2. Table 1 lists colorant compositions derived from vegetable extracts, including beet root, bell peppers, and onion skin. Table 2 lists a series of colorant formulations derived from turmeric, annatto seeds, and/or paprika, together with some purified pigments which were tested for comparison. Curcumin and the colorant formulations derived from turmeric, annatto seeds, and/or paprika were made available to us as gifts from Kalsec, Inc., Kalamazoo, Mich. Bixin, capsanthin, and beetroot extract (betanin) were purchased from Tokyo Kasei Co., Japan through TCI America, Portland, Oreg., USA. Grape extract was supplied by Penta Manufacturing, a division of Penta International Corporation, Fairfield, N.J. Beetroot extract (betanin), grape extract, and capsanthin (derived from paprika) were used without further processing. Red onions, cranberries, long red bell peppers (12 cm long, 7 cm wide at the top, and 5 cm wide at the bottom), short red bell peppers (10 cm long, 7 cm wide at the top, and 4.5 cm wide at the bottom), purple bell peppers, green bell peppers, and light yellow green bell peppers were purchased at a supermarket in Potomac, Md. and used to prepare extracts.

To prepare extracts, the dry skin of onion and the other plant materials (cranberries, long red bell peppers, short red bell peppers, purple bell peppers, green bell peppers, and light yellow green bell peppers) were separately crushed in a blender. In each case, a weighed amount of material was mechanically shaken in a 250 ml flask for 1 hour with 95% ethanol. The mixture was thereafter centrifuged and the supernatant was decanted and filtered. The insoluble residual material was twice reextracted for 20 min by stirring with half the volume of the same solvent as used during the first extraction. The combined extracts were evaporated under a vacuum and weighed, and the percentage yields were recorded. The yield of the dry red onion skin alcoholic extract was 13.2%; that from cranberry was 7.06%; from short red bell pepper 7.06%; and from long red bell pepper 10%.

1.2 Results and Discussion

A wide variety of synthetic colorants were tested for in vitro inhibition of Epstein-Barr virus early antigen induction by TPA. The tested synthetic colorants include:

b) indigo and the following related compounds:

c) the following substituted triphenylmethyl compounds:

d) the following substituted fluorescein compounds:

e) the following anthroquinone derivatives:

f) the pyrene derivative D&C Green No. 8 (XVI); and

g) the following quinoline derivatives:

Each synthetic colorant was tested for activity as an inhibitor of EBV-EA induction in Raji cells according to the previously described method, and the results are recorded in Tables 3 and 4. In each of these tables, the entries have been arranged roughly in order of inhibitory activity toward EBV-EA induction, with the most active colorants being entered first. The tested synthetic colorants have been classified as:

strongly effectively EBV-EA induction inhibitors if all EBV-EA induction is inhibited at a mole ratio of colorant to tumor promoter of 1000 or less;

moderately effective EBV-EA induction inhibitors if the number of Raji cells exhibiting signs of EBV-EA induction in the presence of the colorant (mole ratio of colorant to tumor promotor=1000) is greater than 0% and less than 40% of the number of Raji cells exhibiting signs of EBV-EA induction in the absence of the colorant; and

weakly effective or ineffective EBV-EA induction inhibitors if the number of Raji cells exhibiting sings of EBV-EA induction in the presence of the colorant (mole ratio of colorant to tumor promotor=1000) is greater than 40% of the number of Raji cells exhibiting signs of EBV-EA induction in the absence of the colorant.

The phenylazonaphthalene derivative D&C Red # 33 was found to be the most active among the colorant samples tested in vitro which are included in Table 3, followed by the azo compounds FD&C Yellow # 5 and D&C Red # 7. In fact, it appears that five of the ten most effective colorants included in Table 3 have no azo groups. The results in Table 4, like those in Table 3, indicate that an azo compound is the most active of the colorants included. All of the azo compounds, with the exception of phenazopyridine hydrochloride, appear to show at least moderate anti-tumor promoting activity. While it is interesting to note that phenazopyridine hydrochloride is the only tested azo compound which has no acidic or anionic groups, it is unclear whether this is the cause of its low anti-tumor promoting activity, or merely an interesting coincidence. This would seem to indicate that azo compounds may have therapeutic utility as anti-tumor promoting agents.

The fluorescein colorants showed no clear pattern in their activity, with D&C Red # 22 (the disodium salt of tetrabromofluorescein) showing strong anti-tumor promoting activity, which D&C Yellow # 8, D&C Orange # 5 (dibromofluorescein), D&C Yellow # 7 (fluorescein), and D&C Orange#10 (diiodofluorescein) exhibit moderate anti-tumor promoting activity. Tetrachlorofluorescein, D&C Red # 19 (Rhodamine B), D&C Red # 27 (tetrachlorotetrabromofluorescein), D&C Red # 28 (the disodium salt of D&C Red # 27), and FD&C Red # 3 (the disodium salt of tetraiodofluorescein) were among the least active of the compounds studied.

As for the remaining compounds, the anthroquinone derivatives (carmine, carminic acid, D&C Green No. # 5, and Ext. Violet No. 2) showed strong inhibitory activity toward EBV-EA induction. The quinoline derivative D&C Yellow # 11 was an extremely inactive inhibitor of EBV-EA induction. Surprisingly, however, D&C Yellow # 10 (a sulfonated derivative of D&C Yellow # 10), while not a strong EBV-EA inhibitor, did show significant anti-tumor promoting activity. The pyrene derivative (D&C Green No. 8) and the triphenylmethyl derivatives (FD&C Blue No. 1 and FD&C Green No. 3) were moderately active inhibitors of EBV-EA induction. The indigo-type compound FD&C Blue No. 2 was a strongly effective anti-tumor promoting agent; however, other indigo-type compounds, D&C Blue No. 6 and the alum lake of D&C Red No. 30, were only moderately effective at best. The synthetic colorants studied all exhibited low cytotoxicity.

The vegetable extracts listed in Table 1 were also tested for in vitro inhibition of EBV early antigen induction by TPA, and the results are recorded in Table 5. It is found that the beetroot extract, containing high levels of betanin, inhibits EBV-EA induction by TPA quite strongly. In fact, beetroot extract is more effective at EBV-EA inhibition than capsanthin, a colorant found in paprika. Grape extract was also found to be an effective inhibitor of EBV-EA induction, exhibiting an activity which appears to be greater than that of capsinthin, although not as great as that of beet root extract. Red onion skin extract, although possessing some inhibitory activity toward TPA-induced EBV-EA induction, was found to be less active than beetroot extract, grape extract, or capsanthin, Cranberry and long red onion skin extract. Interestingly, long red bell pepper was the least active of the six extracts studied, while short red and purple bell peppers were the most active, exhibiting slightly greater activity than beetroot extract. The activity of the green and light yellow green bell peppers were roughly as active as red onion skin. It is unclear why the different types of bell pepper extracts have such widely varying activity. None of the vegetable extracts studied showed unacceptable levels of cytotoxicity.

From the above data, it would appear that the beetroot extract, containing betanins as the primary colorants, is an effective inhibitor of EBV-EA induction. More particularly, it seems that betanins are more effective inhibitors of EBV-EA in paprika, or the anthocyanins, the primary colorants in cranberry and red onion skin. The data presented does not allow us to make a clear comparison between the inhibitory activity of betanins and the carotenoids, the primary colorants in both long and short red bell peppers. Nevertheless, the results do seem to indicate that beetroot extracts containing betanins possess potential as inhibitors of TPA-induced tumor formation.

With regard to the vegetable extracts discussed above, it must be noted that it is unproven that the anti-tumor promoting activity is due to colorant compounds. Since the extracts were crude, the anti-tumor promoting activity may be due to a non-colorant compound present in an extract.

The thirty-seven colorant formulations derived from paprika, turmeric, and/or annatto seeds listed in Table 2 were also tested for in vitro inhibition of Epstein-Barr virus early antigen induction by TPA. The results of these tests are recorded in Table 6. Based on the data in Table 6, the colorant formulations have been clarified as:

a) strongly effectively EBV-EA induction inhibitors if:

i) all EBV-EA induction is inhibited at a colorant concentration of 100 micrograms/ml or less; and

ii) the number of Raji cells exhibiting signs of EBV-EA induction in the presence of the colorant formulation (colorant concentration=10 micrograms/ml) is less than 60% of the number of Raji cells exhibiting signs of EBV-EA induction in the absence of the colorant;

b) moderately effective EBV-EA induction inhibitors if:

i) the number of Raji cells exhibiting signs of EBV-EA induction in the presence of the colorant formulation (colorant concentration=100 micrograms/ml) is greater than 0% and less than 50% of the number of Raji cells exhibiting signs of EBV-EA induction in the absence of the colorant; or

ii) all EBV-EA induction is inhibited at a colorant concentration of 100 micrograms/ml; and the number of Raji cells exhibiting signs of EBV-EA induction in the presence of the colorant formulation at a colorant concentration of 10 micrograms/ml is greater than 60% of the number of Raji cells exhibiting signs of EBV-EA induction in the absence of the colorant; and

c) weakly effective or ineffective EBV-EA induction inhibitors if the number of Raji cells exhibiting signs of EBV-EA induction in the presence of the colorant formulation at a colorant concentration of 100 micrograms/ml is greater than 50% of the number of Raji cells exhibiting signs of EBV-EA induction in the absence of the colorant. By applying this system to the results presented in Table 6, the colorant formulations listed in Table 2 have been classified as follows:

strongly active: 1, 2, 4, 9, 11, 15, 16, 19, 20, 21, 22, 24, and 35

moderately active: 3, 5, 6, 7, 12, 13, 14, 17, 18, 23, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 36, and 37

weakly active or inactive: 8 and 10

From the data in table 6, it appears that colorant formulation No. 1, a turmeric extract containing 85-97% curcumin which inhibits all EBV-EA induction at a colorant concentration of 10 micrograms/ml, is the most effective of these compositions as an inhibitor of EBV-EA induction. However, when cell toxicity studies were conducted, it was found that at high concentration of the colorant (100 micrograms/ml), only 20% of the Raji cells used in the EBV-EA activation assay survived exposure to colorant formulation No. 1. In fact, over 45% of the tested compositions derived from paprika, turmeric, and/or annatto seeds showed unacceptably high levels of cytotoxicity (see Table 6). Even if these cytotoxic compositions possess sufficient inhibitory activity toward EBV-EA induction to suggest that they have utility as anti-tumor promoting or cancer chemopreventive agents, the high levels of cytotoxicity raise human health concerns that would argue against their therapeutic use.

Fortunately, several of the compositions derived from paprika, turmeric, and/or annatto seeds showed acceptably low levels of cytotoxicity toward Raji cells in the EBV-EA activation test. At least 60% of the Raji cells exposed to these colorant formulations at a colorant concentration of 100 micrograms/ml survived. Based on the data in Table 6, the non-cytotoxic colorant formulations have been classified in the following manner with regard to their inhibitory activity toward TPA-induced EBV-EA induction:

strongly active: 4, 9, 15, 16, 21, and 35

moderately active: 7, 13, 14, 17, 25, 26, 31, 32, 33, and 34

weakly active or inactive: 8 and 10

Out of the six most effective non-cytotoxic compositions showing anti-tumor activity, two (No. b 4 and No. 35) are composed of natural extractives of annatto seeds and turmeric in a vehicle made from polysorbate 80, KOH, and propylene glycol. The activity of this formulation against EBV-EA induction was greater than that of the annatto seed-derived pigment bixin itself (colorant formulation No. 36) but somewhat less than that of turmeric containing 85-97% curcumin (colorant formulation No. 1). Formulations No. 4 and No. 35 also show much lower cytotoxicity than formulations No. 1 and No. 36, suggesting that therapeutic use of a blend of natural extractives of annatto seeds and turmeric as anti-tumor promoting or cancer chemopreventive agents may pose lower health risks than use of purified pigments from either turmeric or annatto seeds alone. Similarly, colorant formulation No. 21, composed of natural extractives of paprika with vegetable oil showed higher inhibitory activity toward EBV-EA induction than that of the pure paprika-derived pigment capsanthin in vegetable oil (colorant formulation No. 37), coupled with low cytotoxicity. Colorant formulation No. 15, composed of natural extractives of annatto seeds with propylene glycol, water, and KOH, appears to show greater anti-tumor promoting activity and slightly lower cytotoxicity than colorant formulation No. 36, containing the pigment bixin. Interestingly, the activity against EBV-EA induction shown by some natural extractives from paprika and annatto seeds appears to be greater than that of the purified pigments from paprika and annatto seeds.

Other colorant formulations that appear from this data to be particularly effective inhibitors of EBV-EA induction include:

natural extractives of annatto seeds and turmeric in a medium comprising vegetable oil and fumed silicon dioxide; and

extractives of annatto seeds having a norbixin content of 2.6-4.0 wt. % in a medium comprising water and KOH.

2. In Vivo Studies on Inhibition of Carcinogenesis in Mice

2.1. Materials and Methods

Two-stage mouse skin carbinogenesis tests were conducted on mice. Each group of mice was composed of 15 mice housed 5 per cage. Basal diet and tap water were available ad libitum throughout the experiment following the method of Tokuda et al. (Tokuda et al., Oncology, 48, 77-80 [1991]).

Studies on inhibition of TPA-induced skin carbinogenesis by synthetic colorants were conducted on 6-week-old female mice, specific pathogen-free ICR strain, using the following procedure. The back of each mouse was shaved with surgical clippers. Each mouse was then treated topically with 390 nmol 7,12-dimethylbenz[a]anthracene (DMBA) in 0.1 ml acetone. One week before TPA-treatment, each mouse in a test group was treated with an acetone solution of the test dye (85 nM). A control group was not treated with dye. The incidence of papillomas was observed weekly for twenty weeks.

Studies on inhibition of TPA-induced skin carbinogenesis by plant extracts and plant pigments were conducted on 6-week-old female mice, specific pathogen-free ICR strain, using the following procedure. The back of each mouse was shaved with surgical clippers. Each mouse was then treated topically with 390 nmol 7,12-dimethylbenz[a]anthracene (DMBA) in 0.1 ml acetone. After 1 week, each mouse received topically 1.7 nmol TPA in 0.1 ml acetone twice a week for twenty weeks. During TPA treatment, a test group of mice was given drinking water containing a defined test compound, while a control group was given water containing no test compound. For betanin studies a 0.0025% solution of beetroot extract was given orally to the mice (2.5 mg/100 ml H₂O). In studies of paprika and annatto seed extract formulations, the formulations were dissolved in a small volume of ethanol and diluted by water (2.5 mg extract/100 ml H₂O to provide a 0.0025% solution). The incidence of papillomas was observed weekly for twenty weeks.

A similar test was performed for inhibition of ultraviolet radiation-induced skin carbinogenesis. The mice used were 6-week-old female hairless mice, specific pathogen-free Hos:HR-1 strain. Each mouse was treated topically with 390 nmol 7,12-dimethylbenz[a]anthracene (DMBA) in 0.1 ml acetone. After 1 week, each mouse was exposed to UVB radiation for eight minutes twice a week for twenty weeks. The ultraviolet radiation was applied at a dosage of 3,430 J/m². During TPA treatment, a test group of mice was given drinking water containing 0.0025% beetroot extract (2.5 mg extract/100 ml of water), while a control group was given water containing no beetroot extract. The incidence of papillomas was observed weekly for twenty weeks. The lamps used for irradiation of the test mice were Toshiba FL20 S.E. lamps, emitting UV radiation in the 280-320 nm range, with a peak at 305 nm.

Bioassays for inhibition of glycerol-promoted pulmonary tumor formation in mice were also performed. The animals used were ICR male mice. In each group of 15 mice, 0.3 mg of 4-nitroquinoline 1-oxide (4NQO) was injected into the back of each mouse as an initiator. After 5 weeks, a first group of mice was maintained with an 8% glycerol solution as its only source of drinking water. A second group was maintained with 0.0025% betanin solution (2.5 mg/100 ml of 8% glycerol). A third, control group was maintained with water alone. Two additional groups which were not subjected to treatment with 4NQO were also tested. One of these non-4NQO-treated groups was maintained with water alone; the other was maintained with 8% glycerol. After 25 weeks, all mice were sacrificed by cervical dislocation and autopsy was performed. Lung tumors (adenoma) were counted after separation of each pulmonary lobe. Statistical analysis was done using Student's t-test.

The standard mouse ear edema method was followed for the evaluation of anti-inflammatory activity. Indomethacin was used as a control. Seven-week-old ICR male mice were used for the test. On the left side of the mouse's ear, 10 micrograms TPA in 10 microliters acetone were applied. On the right side of the mouse's ear, 10 micrograms TPA and a defined amount of a test compound in 10 microliters acetone were applied. After a defined period of time, a portion of TPA-treated mouse ear was removed and weighed. At the same time, a portion of TPA and test compound-treated mouse ear of the same size and shape as the portion of TPA-treated mouse ear was removed and weighed. Any increase in weight over a section of non-treated mouse ear was taken as a measure of inflammation.

Six-week-old ICR mice and 7-week-old ICR mice were purchased from Japan SLC, Inc., Shizuoka, Japan. Six-week-old Hos:HR-1 mice were purchased from Hoshino Animal Factory, Saitama, Japan. Acetone, DMBA, glycerol, 4NQO, and TPA were purchased from Wako Pure Chemical Industries, Osaka, Japan.

2.2. Results and Discussion

Two of the synthetic colorants tested in vitro inhibition of TPA-induced EBV-EA induction were also studied in vivo to determine whether they inhibited TPA-induced tumor formation in mice. The studies were conducted using a two-stage mouse skin carcinogenesis bioassay. The colorants studied were tartrazine (FD&C Yellow #5), which was among the most active colorants tested in the in vitro EBV-EA induction assay, and erythrosine B (FD&C Red #3), which was one of the least active colorants.

The results are presented in FIG. 2. FIG. 2 shows the percentage of papillomas (or, more precisely, the percentage of mice having papillomas) formed with and without colorant treatment over a period of twenty weeks. The control animals, without the colorant treatment, show 100% incidence of papillomas in less than ten weeks. The test animals, which have been treated with colorant, take 15 weeks to show even 80% papillomas formed per mouse over a fifteen week period (FIG. 2). As seen, both the colorants appear to cause a 40% reduction in the number of papillomas per mouse. Thus, tartrazine and erythrosine B both show inhibitory activity toward TPA-induced two stage skin carcinogenesis.

Beetroot extract (betanin) was also tested for inhibitory activity toward TPA-induced tumor formation in mice using a two-stage mouse skin carcinogenesis bioassay. As shown in FIG. 3, oral ingestion of betanin in ICR mice inhibited TPA-induced promotion of mice skin tumors. Both the percentage of mice having papillomas and the number of papillomas formed per mouse are significantly lower in mice given a betanin solution to drink than they are in mice given substantially pure water.

Oral ingestion of betanin in Hos:HR-1 mice also acts to inhibit UVB radiation-promoted skin carbinogenesis, as shown in FIG. 4. The control animals, drinking water alone, show 100% incidence of papillomas in less than ten weeks of radiation treatment. In the same period, only 25% of the test animals, drinking water containing 0.0025% betanin, show any incidence of tumors. The test animals take 15 weeks to show even 80% papilloma formation. Evidence of anti-tumor activity is also seen in the number of papillomas formed per mouse over a twenty week period. Oral feeding of betanin in drinking water causes a 40% reduction in the number of tumors per mouse, as compared to the number of tumors per mouse in a control group of mice maintained on water alone. The mice in the control group were also fund to show splenomegalia (“hypertrophia spleen”). The test animals, which were fed betanin in drinking water, did not show splenomegalia. FIG. 5 provides a visual comparison of the spleens of mice subjected to UVB radiation treatment for twenty weeks while being maintained on water alone (positive control) and the spleens of mice subjected to radiation treatment while being maintained on water containing 0.0025% betanin. This would seem to indicate that betanin is an effective inhibitor of ultraviolet B irradiation-induced skin tumor formation, and also affords protection against UVB irradiation-induced splenomegalia.

Beetroot extract was also tested for inhibitory activity toward pulmonary tumor formation. As shown in Table 7, oral ingestion of beetroot extract in drinking water containing 8% glycerol leads to a 60% reduction of lung tumors in 4NQO-treated mice, compared to 4NQO-treated mice maintained an an 8% solution of glycerol alone. These findings, together with the findings on skin tumor formation, indicate that beetroot is a useful cancer preventive vegetable.

Two of the colorant formulations derived from turmeric, annatto seeds, and/or paprika were also tested for inhibition of TPA-induced tumor formation in mice, and the results are shown in FIG. 6. A control group of mice maintained on water alone showed 100% incidence of skin tumors in ten weeks. By comparison, a test group of mice maintained on water containing 0.0025% colorant formulation #21, composed of natural extractives of paprika with vegetable oil, showed only 80% incidence of tumors after 15 weeks. A 60% reduction in the number of tumors per mouse was also observed at the end of a twenty week period. Another test group of mice was maintained on water containing 0.0025% colorant formulation #22, composed of natural extractives of annatto seeds with vegetable oil. Formulation #22 was less effective than formulation #21, showing 80% incidence of tumors after only 13 weeks. More tumors per mouse were seen after twenty weeks in mice fed formulation #22 than in those fed formulation #21. Additionally, the in vitro results presented in Table 6 indicate that formulation #21 has significantly lower cytotoxicity than formulation #22. This data would seem to indicate that a composition of natural extractives of paprika with vegetable oil may have potential therapeutic utility as an anti-tumor promoting or cancer chemopreventive agent.

Formulation #21 and formulation #22 were also tested for anti-inflammatory activity by the mouse ear edema method. Both formulations exhibited anti-inflammatory activity, with formulation #21 showing greater activity than #22. The results are provided in Table 8. As can be seen, the extractive of paprika in vegetable oil (formulation #21) exhibited comparatively strong anti-inflammatory activity as compared to indomethacin. The extractive of annatto seeds with vegetable oil (formulation #22) showed lower activity than #21. It is possible that paprika extractives may be therapeutically useful anti-inflammatory agents.

TABLE 1 Vegetable-Derived Colorant Extracts Tested for EBV-EA Inhibition Extract Colorant Ingredient Beet Root Betanins Red Onion Skin Anthocyanins Paprika Capsanthin Cranberry Anthocyanins Short Red Bell Peppers Carotenoids Long Red Bell Peppers Carotenoids Grape Anthocyanins

TABLE 2 Turmeric-, Paprika-, and/or Annatto Seed-Derived Colorant Formulations Tested for EBV-EA Inhibition Colorant Composition Formulation No. (As provided in the product literature)  1 Turmeric, Curcumin Content 85-97%  2 Turmeric, Curcumin Content 29-31%  3 Natural Extractives of Turmeric with not more than 80% Polysorbate 80, KOH, and Antifoam  4 Natural Extractives of Annotta Seeds and Turmeric with Polysorbate 80, KOH, and Propylene Glycol  5 Natural Extractives of Annotta Seeds and Turmeric with Vegetable Oil and Fumed Silicon Dioxide  6 Natural Extractives of Annotta Seeds and Turmeric with Vegetable Oil, Mono-, Di-, and Triglycerides, 7.3% BHT, and Fumed Silicon Dioxide  7 Natural Extractives of Turmeric and Paprika with Vegetable Oil and Fumed Silicon Dioxide  8 Natural Extractives of Annotta Seeds with Water and KOH with Norbixin Content of 1.04-1.16%  9 Extractives of Annatto Seeds with Water and KOH with Norbixin Content of 2.6-2.8% 10 Extractives of Annotta Seeds with Propylene Glycol and KOH with Bixin Content of 2.48-2.67% 11 Natural Extractives of Turmeric with Lecithin, Mono- and Diglycerides, and Vegetable Oil 12 Natural Extractives of Annotta Seeds and Turmeric with Polysorbate 80, KOH, and Propylene Glycol 13 Natural Extractives of Annatto Seeds with Vegetable Oil 14 Natural Extractives of Annatto Seeds with Vegetable Oil, Mono-, Di-, and Triglycerides 15 Natural Extractives of Annatto Seeds and Propylene Glycol, Water, and KOH 16 Natural Extractives of Annatto Seeds and Turmeric with Vegetable Oil and Fumed Silicon Dioxide 17 Natural Extractives of Annatto Seeds with Propylene Glycol, Polysorbate 80, and KOH with Bixin Content of 2.48-2.67% 18 Natural Extractives of Turmeric with Mono-, Di-, and Triglycerides and Propylene Glycol 19 Natural Extractives of Paprika and Turmeric with Vegetable Oil and Fumed Silicon Dioxide 20 Natural Extractives of Turmeric with Propylene Glycol 21 Natural Extractives of Paprika with Vegetable Oil 22 Natural Extractiveness of Annatto Seeds with Vegetable Oil 23 Natural Extractives of Paprika with Mono- and Di-glycerides, Lecithin, and Vegetable Oil 24 Natural Extractives of Turmeric with Polysorbate 80 25 Natural Extractives of Annatto Seeds and Turmeric with Vegetable Oil 26 Natural Extractives of Annatto Seeds and Paprika with Vegetable Oil and Fumed Silicon Dioxide 27 Natural Extractives of Turmeric with Vegetable Oil 28 Natural Extractives of Annatto Seeds with Vegetable Oil and Fumed Silicon Dioxide 29 Natural Extractives of Annatto Seeds with Water and KOH 30 Natural Extractives of Annatto Seeds with Vegetable Oil, Mono- and Di-glycerides and Lecithin 31 Natural Extractives of Annatto Seeds with Propylene Glycol, Water and KOH 32 Natural Extractives of Annatto Seeds with Water and KOH with Norbixin Content of 3.65-4.0% 33 Natural Extractives of Annatto Seeds with Vegetable Oil, Mono-, Di-, and Triglycerides, and KOH 34 Natural Extractives of Annatto Seeds and Paprika with Vegetable Oil, Mono-, Di-, and Triglycerides, and KOH 35 Natural Extractives of Annatto Seeds and Turmeric with Polysorbate 80, KOH, and Propylene Glycol 36 Bixin/Annatto Extract 37 Capsinthin/Paprika Extract in Vegetable Oil

TABLE 3 Inhibitory Effect of Synthetic Colorants on TPA-Induced EBV-EA Induction % relative to control (% viability)* Colorant Concentration (mol ratio/TPA) Colorant 1000 500 100 10 D & C Red # 33 0 (70) 15.5 42.1 88.1 FD & C Yellow # 5 0 (70) 37.1 65.8 89.0 D & C Red # 7 0 (70) 44.7 65.0 89.5 D & C Green # 5 0 (70) 0 66.5 93.7 Olsal 0 (60) 11.2 65.9 100 FD & C Yellow # 6 0 (70) 64.8 72.0 100 Sulfasal 0 (60) 26.9 72.0 100 Carminic Acid 0 (70) 65.8 88.0 100 D & C Orange # 4 0 (70) 18.6 68.3 100 D & C Red # 22 0 (60) 32.5 73.9 100 Ext. D & C 0 (70) 0 87.0 100 Violet # 2 Carmine 0 (70) 26.4 91.5 100 FD & C Blue # 2 0 (70) 43.7 91.4 100 FD & C Red # 40 19.6 (70) 34.8 75.5 100 D & C Orange # 5 24.7 (70) 57.2 82.6 100 D & C Yellow # 7 33.8 (60) 54.0 76.3 100 D & C Green # 8 15.8 (60) 39.3 84.0 100 D & C Yellow # 8 16.7 (60) 52.8 91.6 100 FD & C Blue # 1 12.8 (70) 66.0 93.5 100 D & C Yellow # 10 16.3 (60) 57.0 100 100 D & C Red # 6 32.3 (70) 55.0 81.4 100 D & C Orange # 10 17.9 (70) 81.3 100 100 D & C Blue # 6 25.1 (70) 84.9 100 100 Tetrachloro- 41.3 (60) 63.9 82.0 100 fluorescein D & C Red # 19 43.8 (60) 69.2 85.9 100 D & C Yellow # 8 46.2 (60) 67.3 86.9 100 Phenazo 47.2 (60) 74.6 93.1 100 D & C Red # 21 45.1 (70) 72.6 92.4 100 D & C Red # 28 53.8 (60) 77.4 100 100 FD & C Red # 3 63.5 (70) 85.7 100 100 D & C Yellow # 11 81.5 (70) 100 100 100 D & C Red # 27 88.8 (70) 100 100 100 *Values represent percentages of Raji cells showing EBV-EA induction (error ≦± 3%), measured relative to the positive control value (TPA 32 pmol = 100%). Values in parentheses are viability percentages of Raji cells.

TABLE 4 Inhibitory Effect of Synthetic Colorants on TPA-Induced EBV-EA Induction % relative to control (% viability)* Colorant Concentration (micrograms/ml) Colorant 10 1 0.1 0.01 D & C Red # 39 0 (60) 61.7 88.2 100 FD & C Red # 3 32.4 (70) 64.9 92.0 100 FD & C Blue # 1 32.6 (70) 67.7 90.3 100 FD & C Red # 4 25.6 (60) 87.2 100 — D & C Red 30, 21.4 (70) 90.5 100 100 Al Lake *Values represent percentages of Raji cells showing EBV-EA induction, measured relative to the positive control value (TPA 32 pmol = 100%). Values in parentheses are viability percentages of Raji cells.

TABLE 5 Inhibitory Effect of Vegetable Dye Extracts on TPA-Induced EBV-EA Induction % relative to control (% viability)* Extract Concentration (micrograms/ml) Extract 500 100 10 1 Beet Root 0 (60) 8.3 40 89.4 Grape** — 0 (70) 57.2 85.7 Capsanthin 0 (70) 19.5 54.3 87.5 Cranberry — 45.1 90 100 Red Onion — 0 (60) 65.6 87.2 Skin Long Red Bell — 54.0 (70) 100 100 Pepper Short Red Bell — 0 (70) 25.0 80.4 Pepper Purple Bell — 0 (70) 18.5 85.7 Pepper Green Bell — 0 (70) 63.9 100 Pepper Light Yellow — 0 (70) 79.2 100 Green Pepper *Values represent percentages of Raji cells showing EBV-EA induction, measured relative to the positive control value (TPA 32 pmol = 100%). Values in parentheses are viability percentages of Raji cells. **At 0.1 micrograms/ml extract concentration, the percentage of Raji cells showing EBV-EA induction, measured relative to the positive control value is 100%.

TABLE 6 Inhibitory Effect of Colorants Derived from Paprika, Turmeric, and/or Annatto Seeds on TPA-Induced EBV-EA Induction % relative to control (% viability)* Colorant Colorant Concentration (micrograms/ml) Formulation 100 10 1 Cytotoxic?  1 0 (20) 0 (60) 67.2 yes  2 0 (10) 46.1 (70) 89.4 yes  3 16.4 (0) 42.7 (60) 69.5 yes  4 0 (79) 48.3 67.2 no  5 28.7 (0) 100 (60) 100 yes  6 36.7 (20) 85.3 (70) 100 yes  7 0 (70) 80.1 100 no  8 90.6 (70) 100 100 no  9 0 (70) 44.7 100 no 10 72.8 (70) 93.8 100 no 11 0 (0) 45.9 (60) 93.2 yes 12 0 (0) 64.7 (60) 95.5 yes 13 33.9 (60) 58.0 100 no 14 17.4 (60) 100 100 no 15 0 (60) 36.8 90.2 no 16 0 (60) 57.4 92.5 no 17 30.7 (70) 84.0 100 no 18 10.6 (0) 46.9 (70) 86.1 yes 19 0 (0) 45.4 (70) 73.0 yes 20 0 (0) 58.9 (60) 80.4 yes 21 0 (60) 27.3 77.9 no 22 0 (0) 35.5 (60) 73.0 yes 23 15.7 (0) 59.4 (60) 93.7 yes 24 0 (0) 46.3 (60) 89.6 yes 25 18.6 (80) 100 100 no 26 25.9 (70) 90.6 100 no 27 0 (20) 82.7 (70) 100 yes 28 28.4 (30) 67.6 (70) 100 yes 29 0 (50) 93.0 100 yes 30 0 (50) 75.4 100 yes 31 0 (80) 63.8 100 no 32 0 (70) 64.6 100 no 33 32.6 (80) 66.3 84.9 no 34 45.2 (80) 73.7 92.8 no 35 0 (80) 20.4 85.6 no 36 0 (50) 66.9 (70) 100 yes 37 19.5 54.3 87.5 unknown *Values represent percetnages of Raji cells showing EBV-EA induction, measured relative to the positive control valie (TPA 32 pmol = 100%). Values in parentheses are viability percentages of Raji cells.

TABLE 7 Incidences of pulmonary tumor in mice treated with betarin 8% glycerol % of mice Group Body wt intake (ml/day Total no. of No. of tumor/ with treatment (g) per mouse) tumors mouse tumors I. Water alone 47.6 ± 4.8 8.0 0 0 0 II. 8% glycerol alone 56.4 ± 5.4 8.8 0 0 0 Initiaition + promotion III. 4NQO + water 46.6 ± 4.6 7.9 3 0.2 ± 0.1 6.6 IV. 4NQO + 8% glycerol 55.2 ± 4.9 8.6 50 3.3 ± 0.5 100 V. 4NQO + 8% glycerol + 55.0 ± 5.1 8.6 14 0.9 ± 0.3 40 0.0025% betanin ^(a)Groups of 15 mice were effective numbers at the end of the experiment ^(b)No statistically significant difference were observed between groups by mean intake of drinking. ^(c)The increase in the body weight of the treated mice was not affected by treatment with betanin.

TABLE 8 Anti-Inflammatory Activity of Paprika and Annatto Seed Extracts Conc.* (μg/10 μl acetone) Indomethacin Kal-21 Kal-22 100 μg +++ ++ ++ 10 ++ + − 1 + − − +++ = strongest anti-inflammat. activity ++ = strong activity + = weak activity − = no activity *On left side of the mouse's ear, 10 μg TPA in 10 μl acetone were applied. On right side of the mouse's ear, 10 μg TPA in 10 μl acetone were applied, together with a defined amount of test compound in 10 μl acetone. 

What is claimed is:
 1. A method of reducing the percentage of Epstein-Barr virus genome-carrying cells which exhibit Epstein-Barr virus early antigen induction, wherein said Epstein-Barr virus genome-carrying cells have been cultivated in the presence of at least one chemical selected from the group consisting of a tumor-promoting chemical and a tumor-inducing chemical, said method comprising the steps of: a) cultivating Epstein-Barr virus genome-carrying cells in the presence of a predetermined amount of a chemical selected from the group consisting of a tumor-promoting chemical and a tumor-inducing chemical; and b) treating the Epstein-Barr virus genome-carrying cells with an amount of a synthetic colorant which is effective to reduce the incidence of Epstein-Barr virus early antigen induction in the cultivated Epstein-Barr virus genome-carrying cells, wherein the synthetic colorant is an anthraquinone derivative selected from the group consisting of D&C Green #5, Ext. D&C Violet #2, and mixtures thereof; wherein the predetermined amount of the chemical is sufficient to induce Epstein-Barr virus early antigen induction in Epstein-Barr virus genome-carrying cells which have been cultivated in the presence of the chemical, but have not been treated with the synthetic colorant.
 2. The method of claim 1, wherein the medium contains a tumor-promoting chemical.
 3. The method of claim 1, wherein the medium contains a tumor-inducing chemical.
 4. The method of claim 1, wherein the medium contains a tumor-promoting chemical and a tumor-inducing chemical.
 5. The method of claim 2, wherein the tumor-promoting chemical is 12-O-tetradecanoyl-13-acetate.
 6. The method of claim 3, wherein the tumor-inducing chemical is dimethyl[α]benzanthracene.
 7. The method of claim 4, wherein the tumor-promoting chemical is 12-O-tetradecanoyl-13-acetate and the tumor-inducing chemical is dimethyl[α]benzanthracene.
 8. The method of claim 5, wherein the cells have been cultivated by incubation at 37° C. in 1 ml of an RMPI 1640 medium containing the tumor promoter 12-O-tetradecanoylphorbol-13-acetate in a concentration of 32 pM and butyric acid in a concentration of 4 mM.
 9. The method of claim 8, wherein the synthetic colorant is added to the cultivation medium in a concentration which is between 100 times the 12-O-tetradecanoylphorbol-13-acetate concentration and 1000 times the 12-O-tetradecanoylphorbol-13-acetate concentration.
 10. The method of claim 9, wherein the synthetic colorant is added to the cultivation medium in a concentration which is between 500 times the 12-O-tetracecaonylphorbol-13-acetate concentration and 1000 times the 12-O-tetradecanoylphorbol-13-acetate concentration.
 11. The method of claim 1, wherein the synthetic colorant is D&C Green #5.
 12. The method of claim 1, wherein the synthetic colorant is Ext. D&C Violet #2.
 13. A method of inhibiting Epstein-Barr virus early antigen induction in Epstein-Barr virus genome-carrying cells have been cultivated in an RPMI 1640 medium containing a tumor-inducing chemical and a tumor-promoting chemical, said method comprising the steps of: a) cultivating Epstein-Barr virus genome-carrying cells in the presence of a predetermined amount of a tumor-promoting chemical and a predetermined amount of a tumor-inducing chemical; and b) treating the Epstein-Barr virus genome-carrying cells with an amount of a synthetic colorant which is effective to reduce the incidence of Epstein-Barr virus early antigen induction in the cultivated Epstein-Barr virus genome-carrying cells, wherein the synthetic colorant is selected from the group consisting of an anthraquinone derivative selected from the group consisting of compounds of formula XIII: wherein the predetermined amount of the tumor-promoting chemical and the predetermined amount of the tumor-inducing chemical are in combination sufficient to induce Epstein-Barr virus early antigen induction in Epstein-Barr virus genome-carrying cells which have

been cultivated in the presence of the tumor-promoting chemical and tumor-inducting chemical, but have not been treated with the synthetic colorant.
 14. The method of claim 13, wherein the tumor-promoting chemical is 12-O-tetradecanoylphorbol-13-acetate.
 15. A method of inhibiting Epstein-Barr virus early antigen induction in Epstein-Barr virus genome-carrying cells which have been cultivated in an RPMI 1640 medium containing a tumor-inducing chemical and a tumor promoting chemical by adding an effective amount of a synthetic colorant to the medium, wherein the colorant is a compound of formula X:

wherein R10 is —H or —OH and each R11 is a lower alkyl group.
 16. The method of claim 15, wherein the tumor-promoting chemical is 12-O-tetradecanoylphorbol-13-acetate.
 17. A method of inhibiting Epstein-Barr virus early antigen induction in Epstein-Barr virus genome-carrying cells which have been cultivated in an RPMI 1640 medium containing a tumor-inducing chemical and a tumor promoting chemical by adding an effective amount of a synthetic colorant to the medium, wherein the colorant is selected from the group consisting of: a compound of formula XI:

wherein Y is —H or —Br; and a compound of formula XII:

wherein Z is —H, —Br, or —I.
 18. The method of claim 17, wherein the tumor-promoting chemical is 12-O-tetradecanoylphorbol-13-acetate.
 19. A method of determining the effect of a synthetic colorant on Epstein-Barr virus early antigen induction in Epstein-Barr virus genome-carrying cells which have been cultivated in the presence of a tumor-promoting chemical or a tumor-inducing chemical, said method comprising the steps of: a) cultivating a first group of Epstein-Barr virus genome-carrying cells in the presence of an effective amount of a tumor-promoting chemical or a tumor-inducing chemical, said effective amount being sufficient to induce Epstein-Barr virus early antigen induction; b) cultivating a second group of Epstein-Barr virus genome-carrying cells in the presence of a predetermined amount of tumor-promoting chemical or a tumor-inducing chemical, said predetermined amount being equal to said effective amount; c) treating the second group of Epstein-Barr virus genome-carrying cells, but not the first group of Epstein-Barr virus genome-carrying cells, with a synthetic colorant, where the synthetic colorant is an anthraquinone derivative selected from the group consisting of D&C Green #5, Ext. D&C Violet #2, and mixtures thereof; d) measuring a percentage of Epstein-Barr virus genome-carrying cells in the first group of cells which exhibit Epstein-Barr virus early antigen induction; e) measuring a percentage of Epstein-Barr virus genome-carrying cells in the second group of cells which exhibit Epstein-Barr virus early antigen induction; and f) comparing the percentage of Epstein-Barr virus genome-carrying cells which exhibit Epstein-Barr virus early antigen induction in the first group of cells to the percentage of Epstein-Barr virus genome-carrying cells which exhibit Epstein-Barr virus early antigen induction in the second group of cells. 